Magnetic storage member comprising a carbon layer and directly overcoated fluorolubricant layer

ABSTRACT

The invention provides a magnetic storage member having a magnetic medium coated on a substrate, a protective film coated on the medium, and a lubricant coated on the protective film, the lubricant having a functional group with an inorganic character of 110 or more. The magnetic storage member is provided with the lubricant which can prevent adsorption to a magnetic head, is not removed by sliding with the head and rotation of the magnetic storage member, and has excellent wear resistance.

This is a continuation of application Ser. No. 08/470,709 filed Jun. 6,1995 now U.S. Pat. No. 5,900,318, which is a Continuation of applicationSer. No. 08/266,114 filed Jun. 27, 1994 (now abandoned), which is aContinuation of application Ser. No. 08/044,051 filed Apr. 8, 1993 (nowabandoned).

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to an improved magnetic storage member for use ina magnetic storage unit such as a magnetic disk unit, a magnetic drumunit or the like.

2. Description of the Related Art

Generally, recording and reproducing systems for magnetic storage unitshaving magnetic heads for recording and reproducing (hereinafterreferred to as "head" for simplicity) and magnetic storage member are asfollows. For instance, one of the systems relates to acontact-start-stop system (hereinafter referred to as "CSS" forsimplicity). In the CSS system, at the start of operation, a head isbrought into contact with the surface of a magnetic storage member andthen the magnetic storage member is rotated at a given speed to therebyprovide a spacing due to an air layer created between the head and thesurface of the magnetic storage member, thereby enabling the recordingand reproducing operations. In this system, at the end of operation,rotation of the magnetic storage member stops in a state where the headand the magnetic storage member are maintained in frictional contactwith each other in the same manner as in the start of operation.Frictional power created between the head and the magnetic storagemember, which are maintained in such frictional contact, causes the headand the magnetic storage member to wear out and, in the end, damages thehead and a magnetic medium.

Furthermore, in the state of frictional contact as mentioned above,slight change in position of the head makes load added to the headununiform, whereby the surfaces of the head and magnetic storage memberare in some cases damaged. In addition, when the head and the storagemember come in contact with each other for long time, the head and themagnetic storage member are adsorbed to each other and thus it is hardto separate them from each other.

In order to prevent the magnetic storage member from being destroyed andadsorbed by contact and sliding with the head, the surface of themagnetic storage member (i.e. a protective film) has been coated with alubricant, such as perfluoropolyether or the like, as referred to inJapanese Unexamined Patent Publication No. 52-49805. The publicationdescribes perfluoropolyether having a functional group such as --COOH,--CH₂ OH, --COOCH₃ or a group of the following formula. ##STR1##

The above-mentioned functional groups have inorganic characters of 150,100, 60 and 15, respectively.

However, the lubricants having the above-mentioned functional groupshave weak adsorbability to the protective film and are removed from thesurface of the protective film by repetition of the sliding with thehead or a number of CSS's, or by the centrifugal force caused due to therotation of the magnetic storage member such as the magnetic disk, andthus it is impossible to prevent the magnetic storage member from beingdamaged. In addition, the lubricant thus removed is thickly localized onand adsorbed to the contact sliding surface between the magnetic storagemember and the head and thus it is hard to separate the storage memberand the head from each other.

SUMMARY OF THE INVENTION

It is an object of this invention to provide a magnetic storage memberprovided with a lubricant which can prevent adsorption to a magnetichead, be not removed by sliding with the head, be not removed byrotation of the magnetic storage member and has wear resistance.

The invention provides a magnetic storage member comprising a substrate,a magnetic medium laid on the substrate, a protective film laid on themagnetic medium, and a lubricant laid on the protective film and havinga functional group with an inorganic character of 110 or more.

In a preferred embodiment, the lubricant has the functional group of thefollowing formula: ##STR2## or ##STR3## or mixtures thereof, wherein Grepresents --AsO₃ H₂, J represents >AsO₂ H, >NOH, --SO₂ NHCO--, --NHSO₂NH--, --CONHCONHCO--, --CONHCONH--, --SO₂ NH--, --CSNH--, --NHCONH--,--CONH--, --COOCO-- or lactone ring and U represents >NNH--.

The lactone ring has the following formula: ##STR4##

The above-mentioned functional groups have inorganic characters of 110or more, indicating strength of bond of the functional group to theprotective film. Thus, ability of the functional group which is to beheld on the surface of the magnetic storage member is more superior thanthat of functional groups used in the prior art. The inorganic characteris an index indicating affinity of a functional group as can be seenfrom Pharmaceutical Bulletin, Vol. 2, No. 2, p.163 (1954). That is, theboiling point of derivatives having any functional group is relativelyexpressed on the basis of that of an alcohol derivative of hydrocarbonto be in terms of 100. The above-mentioned functional groups haveinorganic characters of characters 300, 300, 220, 260, 250, 250, 240,240, 230, 220, 200, 110, 120 and 210, respectively.

In the above formula, R_(f) represents --CF₂ (COF₂)_(p) (OC₂ F₄)_(q)OCF₂ --, R_(f) ' represents F(CF(CF₃)CF₂ O)_(p) (OCF₂)_(q) OCF₂ --,F(CF(CF₃)CF₂ O)_(r) CF₂ --, F(C₃ F₆ O)_(r) C₂ F₄ --, C_(n) F_(2n+1) --,C_(n) F_(2n+1) C_(m) H_(2m) --, HC_(k) H_(2k) C_(n) F_(2n) --, HC_(k)H_(2k) C_(n) F_(2n) C_(m) H_(2m) -- or C_(n) H_(2n+1) --, and p, q, rand m are an integer of 1 or more, n is an integer of 3 or more and k iszero or an integer of 1 or more.

The substrate is made of, for instance, an alloy such as an aluminumalloy, titanium alloy, stainless steel or the like; plastic such aspolyester, polyimide, polyamide-imide, polyether sulfone, polysulfone,aromatic polyether, epoxy resin, urea resin, melamine resin,polycarbonate, diallyl phthalate resin, acrylic resin, phenolic resin,polyphenylene sulfide, polyphenylene ether, polyacetal resin,polybutylene terephthalate, bismaleimide triazine resin,polyoxybenzylene resin, polyaminobismaleimide resin, polyphenyleneoxide, polyphenylene sulfide or the likes ceramics such as glass,silicon, germanium, alumina, silica, diamond or the like; an aluminumalloy coated with anodized aluminum; an Ni--P plating film; FeNi; or ametal such as Cr, Mo, W or the like.

The magnetic medium coated on the above-mentioned substrate is made of amagnetic material, for instance, an oxide such as Fe₃ O₄, γ-Fe₂ O₃,barium ferrite, CrO₂ or the like; a nitride such as Fe₃ N₄ or the like;carbide such as Fe₅ C₂ or a the like; Co or a Co-containing metal suchas CoNi, CoNiP, CoMnP, CoMnNiP, CoRe, CoPt, CoNiPt, CoCr, CoCrTa,CoNiRe, CoMnReP, CoFeCr, CoV, CoRu, CoOs, CoPtCr, CoPtV, CoRh, CoCrRh,CoNiMo, CoNiCr, CoNiW, CoSm or the like; Fe-containing metal such asFeNd, FeMg, FeNd, FeAg, FePd, FeTb or the like; or Mn-containing metalsuch as MnAl, MnCuAl or the like. In addition, the magnetic medium mayinclude resin in which finely-divided particles of the above-mentionedmagnetic materials are incorporated and dispersed.

The above-mentioned protective film is made of, for instance, a siliconcompound such as SiO₂, Si₃ N₄, SiC, silicic polymer or the like; a metaloxide such as Al₂ O₃, CoO, Co₃ O₄, Co₂ O₃, α-Fe₂ O₃, Cr₂ O₃, CrO₃, TiO₂,ZrO₂, ZnO, PbO, NiO, MoO₂, SnO₂ or the like; a metal nitride such asTiN, ZrN, CrN, TaN, BN or the like; a metal sulfide such as MoS₂, WS₂,TaS₂ or the like; a metal carbide such as TiC, ZrC, CrC, TaC or thelike; a metal fluoride such as graphite fluoride or the like; a metalsuch as W, Cr, Ir, NiB, NiP, FeCr, NiCr, Sn, Pb, Zn, Tl, Au, Ag, Cu, Ga,Ru, Rh, Mn, Mo, Os or Ta or alloys thereof; a semiconductor such as Si,Ge, B, C (diamond, amorphous or diamond-like carbon or mixtures thereofor graphite-like carbon or mixtures thereof) or the like; or plasticsuch as polytetrafluoroethylene, phenolic resin, polyimide or the like.

The seven functional groups included in the abovementioned lubricant arestrongly adsorbed on the surface of the protective film and thus thosegroups are not easily removed by sliding between the head and themagnetic storage member.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a partially and schematically cross-sectional view of amagnetic storage member of this invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Preferred embodiments of this invention will hereinafter be described inmore detail with reference to FIG. 1. The effects practically achievedby this invention will also be discussed in detail in comparison withComparative Examples. Of course, the invention is not limited to theexamples chosen and it is possible to envisage other variations thereonwithout departing from the scope of the invention.

EXAMPLE 1

An aluminum alloy base was coated with a nickel-phosphorus plating filmand was mirror-finished with surface roughness of 0.02 micrometers toform a substrate 1. A cobalt-nickel-phosphorus alloy was plated on thesubstrate 1 to form a magnetic medium 2 having a thickness of 0.05micrometers. Then, polysilicic acid (silicic polymer) as shown inJapanese Unexamined Patent Publication No. 52-20804 (which correspondsto U.S. Pat. No. 4,154,875), the disclosure of which is herebyincorporated by reference herein, was applied onto the magnetic medium 2by a spin coating method to cover the medium with a film having athickness of 50 nanometers and then was calcined at 250° C. to form aprotective film 3. Thereafter, a Freon (trade name of fluorohydrocarbonmanufactured by Du Pont company, for instance, trichlorofluoromethane,dichlorodifluoromethane, chlorotrifluoromethane, chlorodifluoromethane,etc.) solution of a lubricant having the following structure was appliedonto the protective film 3 by the spin coating method to form alubricating film 4 having a thickness of 2 nanometers, and thus to makemagnetic disks.

Lubricant A: GCF₂ (OCF₂)₁₃ (OC₂ F₄)₈ OCF₂ G wherein G represents --AsO₃H₂.

Lubricant B: F(C₃ F₆ O)₁₃ C₂ F₄ G wherein G is as defined in LubricantA.

Lubricant C: F(CF(CF₃)CF₂ O)₁₅ CF₂ G wherein G is as defined inLubricant A.

Lubricant D: F(CF(CF₃)CF₂ O)₉ CF₂ JCF₂ (OCF₂ (CF₃)CF)₉ F wherein Jrepresents >AsO₂ H, >NOH, --SO₂ NHCH₂ --, --NHSO₂ NH--, --CONHCONHCO--,--CONHCONH--, --SO₂ NH--, --CSNH--, --NHCONH--, --CONH--, --COOCO--,lactone ring.

Lubricant E: F(C₃ F₆ O)₁₀ C₂ F₄ JF₄ C₂ (OF₆ C₃)₁₀ F wherein J is asdefined in Lubricant D.

Lubricant F: C₉ F₁₉ -G wherein G is as defined in Lubricant A.

Lubricant G: C₉ F₁₉ -J-C₉ F₁₉ wherein J is as defined in Lubricant D.

Lubricant H: C₉ F₁₉ C₂ H₄ -G wherein G is as defined in Lubricant A.

Lubricant I: C₉ F₁₉ C₂ H₄ -J-C₂ H₄ C₉ F₁₉ wherein J is as defined inLubricant D.

Lubricant J: HC₁₀ F₂₀ -G wherein G is as defined in Lubricant A.

Lubricant K: HC₁₀ F₂₀ -J-C₁₀ F₂₀ H wherein J is as defined in LubricantD.

Lubricant L: HCH₂ C₈ F₁₆ C₂ H₄ -G wherein G is as defined in LubricantA.

Lubricant M: [F(C₃ F₆ O)₅ C₂ F₄ ]₂ >NNH--C₂ F₄ (OC₃ F₆)₅ F

Lubricant N: [F(CF(CF₃)CF₂ O)_(r) CF₂ --]₂ >NNH--CF₂ (OCF₂ CF(CF₃))_(r)F

Lubricant O: [C₉ F₁₉ C₂ H₄ ]₂ >NNH--C₂ H₄ C₉ F₁₉

Lubricant P: [HCH₂ C₈ F₁₆ C₂ H₄ ]₂ >NNH--C₂ H₄ C₈ F₁₆ CH₃

Lubricant Q: F(CF(CF₃)CF₂ O)₉ CF₂ JC₁₇ H₃₅ wherein J is as defined inLubricant D.

Lubricant R: F(C₃ F₆ O)₁₀ C₂ F₄ JC₈ H₁₇ wherein J is as defined inLubricant D.

Lubricant S: C₉ F₁₉ -J-C₁₇ H₃₅ wherein J is as defined in Lubricant D.

Lubricant T: HC₁₀ F₂₀ -J-C₁₇ H₃₅ wherein J is as defined in Lubricant D.

Lubricant U: [F(C₃ F₆ O)₅ C₂ F₄ ]₂ >NNH--C₈ H₁₇

Lubricant V: [F(CF(CF₃)CF₂ O)_(r) CF₂ --]₂ >NNH--C₈ H₁₇ ##STR5##

The CSS test was done 100,000 times for each magnetic disk thus obtainedto evaluate wear properties thereof, with results that the initialfriction coefficient of 0.1 did not change and no scratch was observedon surfaces of the heads and the magnetic disks. After the CSS test, theheads and the magnetic disks were left to stand for 70 hours and thenthe adsorbability acting therebetween was measured, with results thatthe measured values were the same as those before the shelf test. Inaddition, in order to examine change in the film thickness of thelubricant 4, a test was carried out under 1,000 rpm at a temperature of60° C., with results that reduction in the film thickness was notentirely observed after two months.

EXAMPLE 2

The same procedures as in Example 1 were repeated to fabricate magneticdisks, except that a carbon film is coated on the magnetic medium 2 by asputtering process to form the protective film 3.

The CSS test was done 100,000 times for each magnetic disk thusfabricated to evaluate wear properties thereof, with results that theinitial friction coefficient of 0.2 did not almost change and no scratchwas observed on surfaces of the heads and the magnetic disks. After theCSS test, the heads and the magnetic disks were left to stand for 70hours and then the adsorbability acting therebetween was measured, withresults that the measured values slightly increased by about 1.2 timesthose before the shelf test. In addition, the test was carried out under1,000 rpm at a temperature of 60° C. in the same manner as in Example 1,with results that reduction in the film thickness of the lubricant 4 wasnot entirely observed after two months.

COMPARATIVE EXAMPLE 1

The same procedures as in Example 1 were repreated to fabricate amagnetic disk, except that perfluoropolyether having inorganic characterof zero and having the following structure: F(C₂ F₄ O)₅ (CF₂ O)₁₅ CF₃was used as a lubricant 4 (1 nm thickness).

The CSS test was done 20,000 times for the magnetic disk thus fabricatedto evaluate wear properties thereof, with results that the frictioncoefficient increased by about 7 times that of the initial frictioncoefficient and scratches resulted on the surfaces of the head and themagnetic disk, the scratches reaching the magnetic medium. After the CSStest, the head and the magnetic disk were left to stand for 70 hours andthen the adsorbability acting therebetween was measured, with resultsthat the measured value increased by about 10 times that before theshelf test. In addition, in the same manner as in Example 1, the testwas carried out under 1,000 rpm at a temperature of, 60° C., withresults that the film thickness of the lubricant decreased to zero aftertwo months.

COMPARATIVE EXAMPLE 2

The same procedures were repeated to fabricate a magnetic disk, exceptthat perfluoropolyether having inorganic character of 100 and having thefollowing structure: GCF₂ (OCF₂)₁₃ (OC₂ F₄)₈ OCF₂ G wherein G represents--CH₂ OH, was used as a lubricant 4 (1 nm thickness).

The CSS test was done 20,000 times for the magnetic disk thus fabricatedto evaluate wear properties thereof, with results that the frictioncoefficient increased by about 10 times that of the initial frictioncoefficient and scratches resulted on the surfaces of the head and themagnetic disk, the scratches reaching the magnetic medium. After the CSStest, the magnetic disk was left to stand for 20 days under anatmosphere of a temperature of 40° C. and relative humidity of 80% andthen the friction coefficient was measured, with results that themeasured value increased by about 15 times that before the test. Inaddition, in the same manner as in Example 1, the test was carried outunder 1,000 rpm at a temperature of 60° C., with results that the filmthickness of the lubricant decreased to about one third relative to theinitial film thickness after two months.

As discussed above in detail, the magnetic storage member according tothis invention has low friction coefficient relative to sliding with thehead, very slight change due to the sliding and excellent wearresistance. Furthermore, adsorbability acting between the magneticstorage member and the head does not occur even when the magneticstorage member is in static contact with the head over the period oflong time and thus it is possible to remarkably improve in reliabilityof the conventional magnetic storages members shown in the comparativeexamples.

While this invention has been described in connection with certainpreferred embodiments, it is to be understood that the subject matterencompassed by way of this invention is not to be limited to thosespecific embodiments. On the contrary, it is intended for the subjectedmatter of the invention to include all alternatives, modifications andequivalents as can be included within the spirit and scope of thefollowing claims.

What is claimed is:
 1. A magnetic storage member comprising a substratehaving an aluminum alloy base and a nickel-phosphorus film coated onsaid base, a cobalt-nickel-phosphorus alloy film coated on saidsubstrate, a carbon film coated on said cobalt-nickel-phosphorus alloyfilm and a lubricant coated without an intervening layer, directly onsaid carbon film, said lubricant being a member selected from the groupconsisting of:GCF₂ (OCF₂)₁₃ (OC₂ F₄)₈ OCF₂ G, F(C₃ F₆ O)₁₃ C₂ F₄ G,F(CF(CF₃)CF₂ O)₁₅ CF₂ G, F(CF(CF₃)CF₂ O)₉ CF₂ JCF₂ (OCF₂ (CF₃)CF)₉ F,F(C₃ F₆ O)₁₀ C₂ F₄ JF₄ C₂ (OF₆ C₃)₁₀ F, C₉ F₁₉ -G, C₉ F₁₉ C₂ H₄ -G, C₉F₁₉ C₂ H₄ -J-C₂ H₄ C₉ F₁₉, HC₁₀ F₂₀ -G, HC₁₀ F₂₀ -J-C₁₀ F₂₀ H, HCH₂ C₈F₁₆ C₂ H₄ -G, {F(C₃ F₆ O)₅ C₂ F₄ }₂ >NNH--C₂ F₄ (OC₃ F₆)₅ F,{F(CF(CF₃)CF₂ O)_(r) CF₂ }₂ >NNH--CF₂ (OCF₂ CF(CF₃))_(r) F, {C₉ F₁₉ C₂H₄ }₂ >NNH--C₂ H₄ C₉ F₁₉, {HCH₂ C₈ F₁₆ C₂ H₄ }₂ >NNH--C₂ H₄ C₈ F₁₆ CH₃,F(CF(CF₃)CF₂ O)₉ CF₂ JC₁₇ H₃₅, F(C₃ F₆ O)₁₀ C₂ F₄ JC₆ H₁₇, {F(CF(C₃)CF₂O)_(r) CF₂ --}₂ >NNH--C₈ H₁₇ } {F(C₃ F₆ O)₅ C₂ F₄ }₂ >NNH--C₈ H₁₇,{F(CF₃)CF₂ O)CF₂ --}₂ >NNH--C₈ H₁₇, ##STR6## and ##STR7## wherein Grepresents --AsO₃ H₂, and J represents >AsO₂ H, >NOH, --SO₂ NHCH₂ --,--CONHCONHCO--, --CONHCONH--, --CSNH--, or a lactone ring, and r is aninteger of 1 or more.
 2. The magnetic storage member as defined in claim1, wherein said carbon film is formed by a sputtering process to form aprotective film.